Although the role of structural proteins in the epidermal mechanical barrier is clear, their role in the permeability barrier is unknown. We hypothesize that selected structural and enzymatic proteins; i.e., those that are both regulated by Ca++ and associated with the cornified envelope (CE): involucrin, loricrin, transglutaminase 1 (TG1), pro-fillaggrin, and K1/10, are regulated/required for barrier homeostasis. This proposal will assess which of these proteins are regulated by permeability barrier requirements, and how these CE-associated proteins, in partnership with the lipid bound envelope (LBE) and the lipid-enriched extracellular lamellae, from the permeability barrier. Specifically, in Aim #1 we will determine which CE- associated proteins are regulated by altered barrier requirements, and whether Ca++ regulates their expression, by: a) measuring the time course of mRNA/protein expression for the CE-associated proteins after acute barrier disruption (acetone, tape stripping) and in essential fatty acid deficiency (EFAD) in hairless mice. b) Ascertaining whether changes in extracellular Ca++ (in vivo by sonophoresis and by immersion) modulate expression of the regulated CE protein(s); and the participation of the calcium receptor (CaR) and voltage-sensitive Ca++ channels in these changes. c) Determining whether the transient decrease in CE-associated protein expression facilitates barrier recovery. Using three transgenic over- expressing (involucrin, K6/16, and pro-filaggrin) murine models, and one of these proteins interferes with permeability barrier homeostasis and lamellar body secretion. In Aim #2, we will determine which CE-associated proteins are required for normal barrier homeostasis, and the mechanisms by which alterations in these proteins lead to barrier abnormalities, by: a) Assessing homeostasis in human and murine models with specific deletions or mutations of CE-associated proteins; i.e., in patients with lamellar ichthyosis (LI; TG1 deletion), epidermolytic hyperkeratoses (EHK;K1 or 10 mutation), ichethyosis bullosa of Siemens (IBS; K2e mutation), palmo-plantar keratoderma (NSPPK; K1 mutation), ichthyosis, Keratoderma (NSPPK; K1 mutation), ichthyosis vulgaris (pro-filaggrin deficiency), Vohwinkle's disease (loricrin mutation), plus involucrin and K10 murine knockout animals. b) Assessing the mechanisms whereby CE-associated proteins influence permeability barrier function.